This invention relates to a lubricating oil supply device for vane compressors, and more particularly to a device of this kind which is adapted to lubricate a shaft seal and shaft bearings thereof while cooling them.
Lubricating oil supply devices for vane compressors are known e.g. from Japanese Utility Model Publication (Kokoku) No. 45-30767, Japanese Utility Model Publication (Kokoku) No. 63-25346, etc.
The known lubricating oil supply devices are each designed such that compression medium with lubricating oil mixed therein is supplied under low pressure from a suction side of the compressor to a shaft seal and shaft bearings, before being compressed, to simultaneously cooling and lubricate the shaft seal and the shaft bearings.
On the other hand, a variable capacity compressor has been proposed e.g. by Japanese Provisional Patent Publication (Kokai) No. 62-129593 by the assignee of the present application, which has a control plate for varying the opening degree of refrigerant inlet ports to thereby control the capacity. In the proposed compressor, the control plate and driving means therefor are arranged on the rear side of the compressor for facilitating the maintenance, and accordingly a discharge pressure chamber is arranged on the front side. Consequently, a shaft seal and a shaft bearing on the front side are apt to be heated by compressed compression medium within the discharge pressure chamber, which requires more effective cooling of the shaft seal to prevent the same from being hot and hence having a shortened life.
In order to supply compression medium under low pressure from the suction chamber to the shaft seal and the shaft bearing on the front side to effectively cool them, a lubricating oil supply device has been proposed by Japanese Provisional Patent Publication (kokai) No. 64-3295 by the assignee of the present application, which comprises a first lubricating oil passage extending in the driving shaft of the compressor along the axis thereof and communicating the suction chamber with a shaft seal chamber accommodating a shaft seal and a shaft bearing, and a second lubricating oil passage communicating the shaft seal chamber with a compression chamber on the suction stroke, whereby a cycle of compression medium is formed in which the medium flows from the suction chamber to the compression chamber on the suction stroke through the first lubricating oil passage, the shaft seal chamber, and the second lubricating oil passage, due to negative pressure created within the compression chamber on the suction stroke by the rotation of the vanes.
However, the proposed lubricating oil device thus ultilizing the negative pressure created within the compression chamber has the following disadvantages: When the vanes further rotate so that the compression chamber executes the compression stroke to create positive pressure therein, the above-mentioned cycle of compression medium is no longer formed. The rotational angle range of the vanes, over which the negative pressure is created, is too small to create negative pressure required to supply a sufficient amount of compression medium to the shaft seal chamber, resulting in poor cooling of the shaft seal chamber.
Further, the first lubricating oil passage is formed directly in the driving shaft so that the diameter of the former has to be so small as to assure required strength of the driving shaft, which makes it impossible to obtain satisfactory lubrication.